The present invention relates to a thermal energy storage material.
Certain polymeric materials have been examined in the prior art for thermal energy storage for home heating and cooling applications. A candidate material is a lightly crosslinked high density polyethylene in the form of pellets. The crosslinking is necessary to prevent the pellets from sticking together when heated above the melting point.
The following three methods of controlled chemical crosslinking of high density polyethylene have been reported in Salyer, I. O. and Davison, J. E., "Thermal-Energy Storage in Crosslinked Pellets of High-Density Polyethylene for Home Heating and Cooling via Off-peak Electric Power Utilization," J. Appl. Poly Sci., 28, 2903, 1983. The first method relates to peroxide-initiated, free radical crosslinking. The second and third methods, respectively, relate to vinyl triethoxy silane grafting crosslinking and electron beam crosslinking. In all of these cases, the crosslinks eliminate the melt flow which is desirable for high-temperature form stability. However, undesirably, these processes decrease crystallinity and heat of fusion which is highly desirable for thermal energy storage. All three methods of crosslinking were reported to result in losses of up to thirty percent of the initial heat of fusion
The following United States patents to Anand et al relate to processes and products resulting from the treating of polymers with a cold plasma for fluorinating the surface of the polymer. U.S. Pat. Nos. 4,264,750 and 4,404,256 describe processes and products of this nature for various uses but not as a thermal energy storage material.
Treatment of polymer surfaces with reactive and nonreactive cold plasmas is discussed in the following articles: Baddour, R. F. and Timmins, R. S., eds., "The Application of Plasmas to Chemical Processing", M.I.T. Press, 1967; Hollahan, J. R. and Bell, A. T., eds., "Techniques and Applications of Plasma Chemistry", Wiley, New York, 1974; Boenig, H. V., ed., "Plasma Science and Technology", Cornell University Press, Ithaca, 1982; Boenig, H. V., ed., "Plasma Chemistry and Technology", Technomic Publishing Co., Pennsylvania, 1983; Clark, D. T., Dilks, A. and Shuttleworth, D., "The Application of Plasma to the Synthesis and Surface Modification of Polymers, Polymer Surfaces", Clark, D. T. and Feast, W. J., eds., Wiley, New York, 1978; and Yasuda, H., "Plasma Modification of Polymers", J. Macromol. Sci.-Chem., A10 (3), 15, 1976.